We propose to study the cellular and molecular basis of two implicit memory-dependent phenomena, repetition priming and task-switch cost. Our research is unusual in that it is conducted in a model system that is advantageous for characterizing underlying cellular/molecular mechanisms (i.e., we study a feeding network). Previously, we demonstrated that repetition priming of ingestion is mediated by modulatory peptides released from command-like neurons. These peptides exert second messenger-mediated effects and alter the excitability and firing frequency of neurons that determine response performance. In proposed experiments we will expand our biophysical analyses of modulator-induced currents. Our findings have generated considerable interest since modulatory peptides are likely to be involved in the induction of repetition priming in other systems and species. Other proposed experiments will study implications of repetition priming for task switching. One set of experiments will use a paradigm where one 'task' (ingestion) ends and another (egestion) begins shortly thereafter. Relatively rapid task switching is of interest since it is often accompanied by a cost, e.g., it is more likely that there will be an inappropriat response to stimulus presentation after the switch. We will test a model that postulates it is a consequence of persistent modulation, i.e., effects of modulators released during the priming of one task persist and negatively impact the performance of a subsequent task. This is an attractive hypothesis since it accounts for a common observation -costs associated with task switching are observed in systems that undergo repetition priming. Other experiments will study longer lasting consequences of task switching in the situation where a switch is followed by a return to the original task. Our preliminary data indicate that this paradigm reveals a previously unappreciated benefit of persistent modulation as a mechanism to configure a network. Namely, we suggest that it enables the retention of a primed state during task switching. To conclude, repetition priming and task cost switches are ubiquitous forms of implicit memory that are impaired under certain pathological conditions (e.g., ADHD patients show substantially larger switch costs than non-ADHD patients). Research such as ours, which will determine how repetition priming is mediated, may provide novel perspectives on these disorders.